From cppreference.com
Range adaptor closure objects are
that are callable via the pipe operator: if C is a range adaptor closure object and R is a
, these two expressions are
:
C(R)R|CTwo range adaptor closure objects can be chained by operator| to produce another range adaptor closure object: if C and D are range adaptor closure objects, then C|D produces a range adaptor closure object E with the following properties:
E stores a copy of C and D, direct-non-list-initialized from std::forward<decltype((C))>(C) and std::forward<decltype((D))>(D) respectively. If such initialization is invalid, C|D is also invalid.
Let c and d be the stored copies (with the same constness and value category as E), and R be a
object, the following expressions are
:
d(c(R))R|c|dE(R)R|E// R | (C | D)Notes: operator() is unsupported for volatile-qualified or const-volatile-qualified version of range adaptor object closure types.
Objects whose type is the same as one of the following objects (ignoring cv-qualification) are range adaptor closure objects:
unary range adaptor objects,
the results of binding trailing arguments by range adaptor objects, and
the results of chaining two range adaptor closure objects by operator|.
See also